Q: Is 515,432 a Fibonacci Number?

How is 515,432 not a Fibonacci number?

The Fibonacci Sequence is a series of numbers where you add the previous two numbers together. The product of each is a Fibonacci number.

You start with 0 and add 1 to get the answer 1. You then add 1 + 1 to get 2. Then 2 + 1 to get 3. Then 2 + 3 to get 5, and so on.

To help you see it a little better, the numbers you add together have been color coded:

0 + 1 = 11 + 1 = 21 + 2 = 32 + 3 = 53 + 5 = 85 + 8 = 13

What would be the next Fibonacci number? If you answered 21, you're right. Here's how: You add 8 + 13, which equals 21.
The product of each set of numbers is a Fibonacci number. There are an infinite number of Fibonacci numbers.

So now that we have a little background on what a Fibonacci number is, let's work through it and try to see if 515,432 is a Fibonacci number.

Notice the last equation above (in red). This shows that 515,432 is NOT a Fibonacci number because the sum of the last equation is larger than the number 515,432 and the sum of the equation before it is smaller than the number 515,432.

This is just one way to find a Fibonacci number and is arguably the easiest to understand. There are many ways to calculate a Fibonacci number. Take a look at
Wikipedia for more information.